Accessory device, imaging apparatus, and communication control program

ABSTRACT

An imaging apparatus that provides, between itself and an accessory device, a notification channel used for notification from the imaging apparatus to the accessory device, a first data communication channel used in data transmission from the accessory device to the imaging apparatus, and a second data communication channel used in data transmission from the imaging apparatus to the accessory device. An accessory control unit transmits data via the first data communication channel in response to having received a transmission request signal via the notification channel, and selectively adds, to the data, a communication standby request for keeping a transmission request signal from being transmitted from the imaging apparatus to the accessory device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/866,348, which was filed on May 4, 2020 and which is a continuationof U.S. application Ser. No. 16/144,897, now issued as U.S. Pat. No.10,785,399, which was filed on Sep. 27, 2018 and which is a continuationof International Patent Application No. PCT/JP2017/012368, which wasfiled on Mar. 27, 2017 and which claims priority to Japanese PatentApplication No. 2016-072984, which was filed on Mar. 31, 2016, all ofwhich are hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to an imaging apparatus, and an accessorydevice such as an interchangeable lens or the like, which arecommunicable with each other.

BACKGROUND ART

There are known lens-replacement type camera systems where an imagingapparatus, which is the camera main body, performs imaging processingand lens control, and lens devices which are interchangeable lensesperform lens driving in accordance with control commands from the cameramain body. In such camera systems, transmission of control commands fromthe camera main body to the interchangeable lens, and transmission oflens information from the interchangeable lens to the camera main body,are performed via a communication channel for exchanging informationwith each other.

Of such lens-replacement type camera systems, digital camera systems inparticular require smooth lens control in accordance with imaging cycleswhen shooting moving images or taking live view images. Accordingly, theimaging timing of the camera main body and the control timing of theinterchangeable lens need to be synchronized, and the camera main bodyneeds to complete obtaining of lens information necessary for lenscontrol and transmission of control commands to the interchangeable lenswithin an imaging cycle.

On the other hand, advanced imaging technology has led to increase inthe data amount of lens information that the camera main body obtainsfrom the interchangeable lens, and frame rates are faster. Accordingly,there is need to communicate great amounts of data in a shorter timethan conventionally.

PTL 1 discloses a clock-synchronized communication system made up ofthree channels, which are a clock channel, a data transmission channelfrom the camera main body to the interchangeable lens, and a datatransmission channel from the interchangeable lens to the camera mainbody. In this communication system, the camera main body serves as acommunication master to generate clock signals, and outputs one frame ofclock signals to the interchangeable lens via the clock channel.Thereafter, the input and output of the clock channel are switched, andthe interchangeable lens that is the communication master instead of thecamera main body outputs a transmission standby request to the samechannel. Accordingly, the interchangeable lens can notify the cameramain body that it is in a processing standby state after communication.

CITATION LIST Patent Literature

-   PTL 1 Japanese Patent Laid-Open No. 9-304804

According to the communication system disclosed in PTL 1, thecommunication master needs to be switched by time management between thecamera main body that outputs clock signals and the interchangeable lensthat outputs communication standby requests over the same channel.Accordingly, there is a need to provide time for switching thecommunication master in order to prevent collision of communication,i.e., a communication-invalid time during which communication cannot beperformed, which as a result may lead to delay in communication andcontrol.

Stopping output of communication standby request signals to the clockchannel by the interchangeable lens to solve this problem results in theinterchangeable lens not being able to make communication standbyrequests to the camera main body at all. If large amounts of data arecommunicated without outputting communication standby request signals,there is a concern of communication breakdown occurring in cases where areception buffer overflow occurs at the interchangeable lens that is thecommunication slave, or where data to be transmitted to the camera mainbody is not generated in time. Also, providing a new channel to outputcommunication standby request signals increases electric powerconsumption, and reduction in size of the camera main body andinterchangeable lens is inhibited.

It is an object of the present invention to realize an accessory deviceand imaging apparatus capable of performing high-speed data exchangewithout leading to breakdown of communication, without adding newchannels.

SUMMARY OF INVENTION

An accessory device according to the present invention is an accessorydevice detachably mounted to an imaging apparatus, having an accessorycommunication unit that provides, between itself and the imagingapparatus, three channels made up of a notification channel used fornotification from the imaging apparatus to the accessory device, a firstdata communication channel used in data transmission from the accessorydevice to the imaging apparatus, and a second data communication channelused in data transmission from the imaging apparatus to the accessorydevice, and an accessory control unit that performs control of theaccessory communication unit. The accessory control unit transmits datato the imaging apparatus via the first data communication channel, inaccordance with having received a transmission request signal via thenotification channel. The accessory control unit selectively adds, todata to be transmitted to the imaging apparatus, a communication standbyrequest for keeping the transmission request signal from beingtransmitted from the imaging apparatus to the accessory device.

An imaging apparatus according to the present invention is an imagingapparatus to which an accessory device is detachably mounted, having ancamera communication unit that provides, between itself and theaccessory device, three channels made up of a notification channel usedfor transmission of a transmission request signal from the imagingapparatus to the accessory device, a first data communication channelused in data transmission from the accessory device to the imagingapparatus, and a second data communication channel used in datatransmission from the imaging apparatus to the accessory device, and acamera control unit that performs control of the camera communicationunit. The camera control unit stops transmission of the transmissionrequest signal while receiving, from the accessory device via the firstdata communication channel, a communication standby request to keep thetransmission request signal from being transmitted.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating the configuration of a camerasystem including an imaging apparatus and an accessory device accordingto the present invention.

FIG. 2 is a schematic diagram illustrating communication circuitsbetween the imaging apparatus and accessory device.

FIGS. 3A through 3C are schematic diagrams illustrating communicationwaveforms in a communication mode M1.

FIG. 4 is a schematic diagram illustrating communication waveforms in acommunication mode M2.

FIGS. 5A through 5C are schematic diagrams illustrating communicationwaveforms in a communication mode M3.

FIG. 6 is a flowchart for describing a flow for deciding a communicationformat at the accessory device and imaging apparatus.

FIG. 7 is a flowchart for describing a data communication flow incommunication method M2.

DESCRIPTION OF EMBODIMENTS

A communication control method in an interchangeable lens serving as anaccessory device and a camera main body serving as an imaging apparatusaccording to the present invention will be described in detail withreference to the attached drawings. First, definition of terms in thepresent embodiment will be described.

“Communication format” indicates rules regarding the entirecommunication between the camera main body and the interchangeable lens.“Communication method” means the clock-synchronized method andasynchronous method, with the clock-synchronized method beingcommunication method A and the asynchronous method being communicationmethod B. “Data format” indicates whether or not a communication standbyrequest signal (BUSY signal) is added, with a data format where adding aBUSY signal is permitted is “format F1”, while a data format whereadding a BUSY signal is forbidden is “format F2”.

“Communication mode” means a combination of communication method anddata format, and the following three communication modes will bedescribed in the present embodiment. “Communication mode M1” is acommunication mode of communication method A and format F1, and“communication mode M2” is a communication mode of communication methodB and format F1. “Communication mode M3” is a communication mode ofcommunication method B and format F2.

The present invention relates to communication control between thecamera main body and interchangeable lens in the communication mode M2.An imaging system having a camera main body and interchangeable lenscapable of communicating by switching between multiple communicationmodes including the communication mode M2 is illustrated in thefollowing embodiment. Appropriately switching the communication mode andperforming communication in this way enables an appropriatecommunication mode to be selected in accordance with the combination ofcamera main body and interchangeable lens, and the shooting mode.

For example, in a case where the camera main body and interchangeablelens are compatible with the communication mode M3, and are to exchangegreat amounts of data, the communication mode of each is switched to thecommunication mode M3, and thereafter high-speed data communication isexecuted where attaching BUSY signals is forbidden. In a case where dataprocessing requires a certain amount of time at the interchangeablelens, the communication mode of each of the camera main body andinterchangeable lens is switched to the communication mode M2, andthereafter data communication is executed where attaching BUSY signalsis permitted. Thus, data communication can be executed between thecamera main body and interchangeable lens that does not lead tobreakdown of communication.

FIG. 1 illustrates the configuration of an imaging system (hereinafterreferred to as camera system) including a camera main body 200 servingas an imaging apparatus that is the first embodiment of the presentinvention, and an interchangeable lens 100 serving as an accessorydevice detachably mounted thereto.

The camera main body 200 and interchangeable lens 100 performtransmission of control commands and internal information viacommunication units that each has. Each communication unit supportsmultiple communication formats, and is capable of selecting an optimalcommunication format under various situations by synchronously switchingto the same communication format as each other in accordance with thetype of communication data and purpose of communication.

First, a specific configuration of the interchangeable lens 100 andcamera main body 200 will be described. The interchangeable lens 100 andcamera main body 200 are mechanically and electrically connected via amount 300 that is a coupling mechanism. The interchangeable lens 100receives supply of power from the camera main body 200 via power sourceterminal, omitted from illustration, provided to the mount 300, andcontrols later-described actuators of various types, and a lensmicroprocessor 111. The interchangeable lens 100 and camera main body200 communicate with each other via communication terminals (illustratedin FIG. 2) provided to the mount 300.

The interchangeable lens 100 has an imaging optical system. The imagingoptical system includes, in order from an object OBJ side, a field lens101, a zoom lens 102 that changes zoom power, a diaphragm unit 114 thatadjusts the quantity of light, an image stabilization lens 103, and afocus lens 104 that performs focal point adjustment.

The zoom lens 102 and focus lens 104 are respectively held by lensholding frames 105 and 106. The lens holding frames 105 and 106 aremovably guided in the optical axis direction, illustrated in the diagramas a dotted line, by a guide shaft omitted from illustration, and aredriven in the optical axis direction by respective stepping motors 107and 108. The stepping motors 107 and 108 move the zoom lens 102 andfocus lens 104 synchronously with driving pulses.

The image stabilization lens 103 reduces image blurring due to shakingof hands and so forth, by moving in a direction orthogonal to theoptical axis of the imaging optical system.

The lens microprocessor 111 is an accessory control unit for controllingoperations of the parts within the interchangeable lens 100. The lensmicroprocessor 111 receives control commands transmitted from the cameramain body 200, and receives transmission requests for lens data, via alens communication unit 112 serving as an accessory communication unit.The lens microprocessor 111 performs lens control corresponding to thecontrol commands, and transmits lens data corresponding to transmissionrequests to the camera main body 200 via the lens communication unit112.

The lens microprocessor 111 also outputs driving signals to a zoom drivecircuit 119 and focus drive circuit 120, in response to commandsrelating to zooming and focusing, out of the control commands, therebydriving the stepping motors 107 and 108. Accordingly, zoom processingwhere zooming operations by the zoom lens 102 are controlled, andautofocus processing where focal point adjustment operations by thefocus lens 104 are controlled, are carried out.

The diaphragm unit 114 is configured including diaphragm blades 114 aand 114 b. The state of the diaphragm blades 114 a and 114 b is detectedby a Hall effect device 115, and input to the lens microprocessor 111via an amplifying circuit 122 and an A/D conversion circuit 123. Thelens microprocessor 111 outputs drive signals to a diaphragm drivediaphragm circuit 121 based on input signals from the A/D conversioncircuit 123, and drives a diaphragm actuator 113. Accordingly, lightquantity adjustment operations by the diaphragm unit 114 are controlled.

Further, the lens microprocessor 111 drives an anti-vibration actuator126 via an anti-vibration drive circuit 125 in accordance with shakingdetected by an unshown shaking sensor such as a vibration gyro or thelike provided within the interchangeable lens 100. Accordingly,anti-vibration processing that controls shifting operations of the imagestabilization lens 103 is performed.

The camera main body 200 has an imaging device 201 such as a CCD sensoror CMOS sensor or the like, an A/D conversion circuit 202, a signalprocessing circuit 203, a recording unit 204, a camera microprocessor205, and a display unit 206.

The imaging device 201 performs photoelectric conversion of a subjectimage formed by the imaging optical system within the interchangeablelens 100, and outputs electric signals (analog signals). The A/Dconversion circuit 202 coverts analog signals from the imaging device201 into digital signals. The signal processing circuit 203 subjectsdigital signals from the A/D conversion circuit 202 to various types ofimage processing, and generates video signals.

The signal processing circuit 203 also generates luminance informationindicating the contrast state of the subject image from the videosignals, i.e., focus information indicating the focal state of theimaging optical system and the exposure state. The signal processingcircuit 203 outputs the video signals to the display unit 206, and thedisplay unit 206 displays the video signals as a live preview image usedfor confirming the composition, focus state, and so forth, of the videosignals.

The camera microprocessor 205 serving as a camera control unit performscontrol of the camera main body 200 in accordance with input from cameraoperating members, such as an imaging instructing switch, various typesof setting switches, and so forth, that are omitted from illustration.The camera microprocessor 205 also transmits control commands relatingto zooming operations of the zoom lens 102 in accordance with operationof an unshown zoom switch to the lens microprocessor 111, via a cameradata transmission/reception unit 208. The camera microprocessor 205further transmits control commands relating to light quantity adjustmentoperations of the diaphragm unit 114 in accordance with luminanceinformation, and focal point adjustment operations of the focus lens 104in accordance with focus information, to the lens microprocessor 111 viathe camera data transmission/reception unit 208 b.

Next, communication circuits configured between the camera main body 200and interchangeable lens 100, and communication control performedtherebetween, will be described with reference to FIG. 2. The cameramicroprocessor 205 has a function of managing communication formatsbetween itself and the lens microprocessor 111, and a function ofnotifying the lens microprocessor 111 of transmission requests and soforth. The lens microprocessor 111 also has a function of generatinglens data and a function of transmitting the lens data.

The camera microprocessor 205 and lens microprocessor 111 performcommunication through communication terminals provided to the mount 300,and communication interface circuits 208 a and 112 a provided to eachrespectively. Here, the communication interface circuit 208 a and cameradata transmission/reception unit 208 b will be collectively referred toas a camera communication unit 208, and the communication interfacecircuit 112 a and a lens data transmission/reception unit 112 b will becollectively referred to as the lens communication unit 112.

In the present embodiment, the camera microprocessor 205 and the lensmicroprocessor 111 perform serial communication by three-linecommunication method A and communication method B using three channels.

One of the above-described three channels is the clock channel in thecommunication method A, and is a notification channel serving as atransmission request channel in the communication method B. One of theremaining two channels is a first data communication channel (accessorydata communication channel) that is used for lens data transmission fromthe lens microprocessor 111 to the camera microprocessor 205. The otherone channel is a second data communication channel (imaging apparatusdata communication channel) used for transmission of camera data fromthe camera microprocessor 205 to the lens microprocessor 111.

Lens data transmitted from the lens microprocessor 111 to the cameramicroprocessor 205 as signals over the first data communication channelwill be referred to as lens data signals DLC. Camera data transmittedfrom the camera microprocessor 205 to the lens microprocessor 111 assignals over the second data communication channel will be referred toas camera data signals DCL.

First, communication by the communication method A will be described. Inthe communication method A, clock signals LCLK are output from thecamera microprocessor 205 serving as the communication master to thelens microprocessor 111 serving as a communication slave, via the clockchannel. The camera data signals DCL include control commands,transmission request commands, and so forth, from the cameramicroprocessor 205 to the lens microprocessor 111. On the other hand,the lens data signals DLC include various types of data transmitted fromthe lens microprocessor 111 to the camera microprocessor 205synchronously with the clock signals LCLK. The camera microprocessor 205and the lens microprocessor 111 are capable of communicating by thefull-duplex communication system where transmission and reception isperformed mutually and simultaneously in synchronization with commonclock signals LCLK.

FIGS. 3A through 3C illustrate waveforms of signals exchanged betweenthe camera microprocessor 205 and lens microprocessor 111. Rules decidedfor procedures for this exchange are referred to as a communicationprotocol.

FIG. 3A illustrates signal waveforms of one frame, that is the smallestincrement of communication. First, the camera microprocessor 205 outputsclock signals LCLK of which clock pulses of eight cycles is one set, andtransmits camera data signals DCL to the lens microprocessor 111synchronously with the clock signals LCLK. At the same time, the cameramicroprocessor 205 receives the lens data signals DLC output from thelens microprocessor 111 synchronously with the clock signals LCLK.

Thus, one byte (eight bits) of data is transmitted and received betweenthe lens microprocessor 111 and camera microprocessor 205 synchronouslywith the ones set of clock signals LCLK. The period fortransmission/reception of one byte of data is called a data frame. Aftertransmission/reception of this one byte of data, the lens microprocessor111 transmits a signal notifying a communication standby request BUSY tothe camera microprocessor 205 (hereinafter referred to as a BUSYsignal), whereby a communication standby period is inserted. Thiscommunication standby period is referred to as a BUSY frame, and thecamera microprocessor 205 is in a communication standby state whilereceiving the BUSY frame. A communication increment of one set of dataframe period and BUSY fame period makes of one frame. Depending on thecommunication state, there are cases where no BUSY frame is added, inwhich cases one frame is made up of just the data frame period.

FIG. 3B illustrates the signal waveforms when the camera microprocessor205 transmits a request command CMD1 to the lens microprocessor 111, andreceives corresponding two-byte lens data DT1 (DT1 a, DT1 b) from thelens microprocessor 111. FIG. 3B illustrates an example of datacommunication being executed in accordance with “communication CMD1”.

Types of lens data DT and byte counts corresponding to each of multipletypes of commands CMD are stipulated beforehand regarding the cameramicroprocessor 205 and lens microprocessor 111. When the cameramicroprocessor 205 that is the communication master transmits aparticular command CMD to the lens microprocessor 111, the lensmicroprocessor 111 transmits a clock count that is necessary based onthe lens data byte count corresponding to this command CMD to the cameramicroprocessor 205. The processing of the lens microprocessor 111 inaccordance with the command CMD1 includes superimposing a BUSY signal onthe clock signals LCLK in each frame, with the above-described BUSYframe being inserted between the data frames.

In communication CMD1, the camera microprocessor 205 transmits clocksignals LCLK to the lens microprocessor 111, and further transmits arequest command CMD1 requesting transmission of lens data DT1 to thelens microprocessor 111 as camera data signals DCL. The lens datasignals DLC in this frame is handled as invalid data.

Next, after having output eight cycles of clock signals LCLK over theclock channel, the camera microprocessor 205 switches the clock channelat the camera microprocessor side (camera main body side) from outputsettings to input settings. Upon the switching of the clock channel atthe camera microprocessor side being completed, the lens microprocessor111 switches the clock channel at the lens microprocessor 111 side(interchangeable lens side) from input settings to output settings. Thelens microprocessor 111 then sets the voltage level of the clock channelto Low, to notify the camera microprocessor 205 of a communicationstandby request BUSY. Accordingly, a BUSY signal is superimposed on theclock channel. During the period in which the communication standbyrequest BUSY is being notified, the camera microprocessor 205 maintainsinput settings of the clock channel, and stops communication to the lensmicroprocessor 111.

The lens microprocessor 111 generates lens data DT1 corresponding to thetransmission request command CMD1 during notification of thecommunication standby request BUSY. Upon preparation for transmittingthe lens data DT1 as the lens data signals DLC of the next frame, thesignal level of the clock channel at the lens microprocessor side isswitched to High, and the communication standby request BUSY iscancelled.

Upon recognizing the cancellation of the communication standby requestBUSY, the camera microprocessor 205 transmits one frame of clock signalsLCLK to the lens microprocessor 111, thereby receiving lens data DT1 afrom the lens microprocessor 111. The camera microprocessor 205 that hasoutput eight cycles of clock signals LCLK again in the next frame, andthe lens microprocessor 111 repeats the same operations as describedabove, whereby the camera microprocessor 205 receives lens data DT1 bfrom the lens microprocessor 111.

FIG. 3C illustrates signal waveforms when the camera microprocessor 205transmits a request command CMD2 to the lens microprocessor 111 andreceives three bytes of lens data DT2 (DT2 a through DT2 c)corresponding thereto from the lens microprocessor 111. FIG. 3Cillustrates an example of data communication being executed inaccordance with communication CMD2. The processing of the lensmicroprocessor 111 in accordance with the request command CMD2 in thiscommunication CMD2 includes superimposing a BUSY signal on the clockchannel only in the first frame. That is to say, the lens microprocessor111 does not superimpose a BUSY signal on the subsequent second framethrough fourth frame.

Accordingly, no BUSY frame is inserted between frames from the secondframe through the fourth frame, and the standby period between framescan be reduced. However, the lens microprocessor 111 cannot transmit acommunication standby request to the camera microprocessor 205 duringperiods where BUSY frames are not inserted. Accordingly, the data countfor transmission, transmission intervals, the order of priority ofcommunication processing within the lens microprocessor 111, and soforth, need to be decided beforehand, so that there is no breakdown ofcommunication as a result.

Next, the communication method B will be described. The communicationmode M2 where communication is performed by format F1 using thecommunication method B will be described as well. FIG. 4 illustrateswaveforms of communication signals exchanged between the cameramicroprocessor 205 and the lens microprocessor 111 in the communicationmode M2. A BUSY frame is selectively added to the lens data signals DLCin the format F1, as described earlier.

The transmission request channel is used for notification of lens datatransmission requests and so forth, from the camera microprocessor 205serving as the communication master to the lens microprocessor 111serving as a communication slave, in the communication method B.Notification over the transmission request channel is performed byswitching the level (voltage level) of signals on this transmissionrequest channel between High (first level) and Low (second level). Inthe following description, signals supplied to the transmission requestchannel in the communication method B will be referred to astransmission request signals RTS.

The first data communication channel is used for transmission of lensdata signals DLC including various types of data from the lensmicroprocessor 111 to the camera microprocessor 205, in the same way aswith the communication method A. The second data communication channelis also used for transmission of camera data signals DCL includingcontrol commands and transmission request commands and so forth from thecamera microprocessor 205 to the lens microprocessor 111, in the sameway as in communication method A.

Unlike the communication method A, the camera microprocessor 205 andlens microprocessor 111 have the communication speed set beforehand andtransmit/receive at a communication bitrate based on this setting in thecommunication method B, instated of performing datatransmission/reception synchronously with common clock signals. Thecommunication bitrate indicates the amount of data that can betransmitted per second, and the unit is expressed as bps (bits persecond).

Note that in the present embodiment, the camera microprocessor 205 andlens microprocessor 111 communicate by the full-duplex communicationsystem where mutual transmission/reception is performed in thiscommunication method B, in the same way as with the communication methodA.

FIG. 4 illustrates signal waveforms of one frame, that is the smallestincrement of communication. The breakdown of the data format of oneframe partially differs between the camera data signals DCL and lensdata signals DLC.

First, the data format of the lens data signals DLC will be described.One frame of lens data signals DLC is made up of the data frame at thefirst half and the subsequent BUSY frame. The signal level of the lensdata signals DLC is maintained at High in a state where datatransmission is not being performed.

The lens microprocessor 111 sets the voltage level of the lens datasignals DLC to LOW for a period of one bit, in order to notify thecamera microprocessor 205 of the start of transmission of one frame ofthe lens data signals DLC. This one-bit period is called a start bit ST,and the data frame is started from the start bit ST. The lensmicroprocessor 111 subsequently transmits one byte of lens data in aneight-byte period from the second bit following the start bit ST throughthe ninth bit.

The array of data bits is an MSB (Most Significant Bit)-first format,starting from the highest order data D7, continuing in order to data D6,data D5, and ends on the lowest order data DO. The lens microprocessor111 then adds one bit of parity information (PA) at the tenth bit, andsets the voltage level of the lens data signals DLC to HIGH for theperiod of a stop bit SP indicating the last of one frame. Thus, the dataframe period started from the start bit ST is ended. Note that theparity information does not have to be one bit, and that parityinformation of multiple bits may be added. The parity information is notindispensable either, and a format may be used where parity informationis not added.

Next, the lens microprocessor 111 adds a BUSY frame after the stop bitSP, as indicated by “DLC (WITH BUSY)” in the drawing. The BUSY frameindicates the period of communication standby request BUSY where thelens microprocessor 111 notifies the camera microprocessor 205, in thesame way as in the communication method A. The lens microprocessor 111maintains the signal level of the lens data signals DLC to Low, untilthe communication standby request BUSY is cancelled.

On the other hand, there are cases where notification of communicationstandby request BUSY from the lens microprocessor 111 to the cameramicroprocessor 205 is unnecessary. Accordingly, a data format where oneframe is configured without adding a BUSY frame (hereinafter alsoreferred to as BUSY notification) is also provided for such cases, asindicated by “DLC (WITHOUT BUSY)” in the drawing. That is to say,selection can be made regarding the data format of the lens data signalsDLC between one with a BUSY notification added and one not added, inaccordance with the processing situation at the lens microprocessorside.

Description will be made regarding the method of the cameramicroprocessor 205 identifying between whether or not there is a BUSYnotification. The signal waveform indicated in “DLC (WITHOUT BUSY)” inFIG. 4 and the signal waveform indicated in “DLC (WITH BUSY)” in FIG. 4include bit positions B1 and B2. The camera microprocessor 205 selectsone of the bit positions B1 and B2 as a BUSY identification position Pfor identifying whether or not there is a BUSY notification. In thisway, the present embodiment employs a data format where the BUSYidentification position P is selected from bit positions B1 and B2.Thus, the problem of different processing times from transmission of thelens data signals DLC data frame until the BUSY notification (DLC isLow) is finalized, depending on the processing capabilities of the lensmicroprocessor 111, can be handled.

Whether the bit position B1 or the bit position B2 is to be the BUSYidentification position P is decided by communication between the cameramicroprocessor 205 and lens microprocessor 111 before performingcommunication by communication method B. Note that the BUSYidentification position P does not need to be fixed to one bit positionof B1 and B2, and may be changed in accordance with the processingcapabilities of the camera microprocessor 205 and lens microprocessor111. Also note that the BUSY identification position P is not restrictedto B1 or B2, and may be set at a predetermined location after the stopbit SP.

Now, the reason why the BUSY frame added to the clock signals LCLK incommunication method A is added to the lens data signals DLC incommunication method B as a data format will be described.

In the communication method A, the clock signals LCLK output by thecamera microprocessor 205 that is the communication master and the BUSYsignal output by the lens microprocessor 111 that is a communicationslave need to be exchanged over the same clock channel. Accordingly,collision of the outputs of the camera microprocessor 205 and lensmicroprocessor 111 is prevented by time division. That is to say,collision of the outputs can be prevented by appropriately assigningoutputtable periods for the camera microprocessor 205 and lensmicroprocessor 111 in the clock channel.

However, in this time division method, collision of the outputs of thecamera microprocessor 205 and lens microprocessor 111 needs to beprevented in a sure manner. To this end, a certain output-forbiddenperiod where output of the microprocessors 205 and 111 is forbidden isinserted between the point in time at which the camera microprocessor205 has completed output of the eight pulses of clock signals LCLK andthe point in time at which output of a BUSY signal by the lensmicroprocessor 111 is permitted. This output-forbidden period is acommunication invalid period where the camera microprocessor 205 andlens microprocessor 111 cannot communicate, and thus leads todeterioration of effective communication speed.

In order to solve this problem, the communication method B employs thedata format where the BUSY frame from the lens microprocessor 111 isadded to the lens data signals DLC on the first data communicationchannel, which is a dedicated output channel for the lens microprocessor111.

Next, the data format of the camera data signals DCL will be described.The specification of one data frame is the same as with the lens datasignals DLC. However, adding of the BUSY frame to the camera datasignals DCL is forbidden, unlike the lens data signals DLC.

Next, the procedures of communication by the communication method Bbetween the camera microprocessor 205 and lens microprocessor 111 willbe described. First, when an event occurs to start communication withthe lens microprocessor 111, the camera microprocessor 205 sets thevoltage level of the transmission request signals RTS to Low(hereinafter, this will be referred to as asserting a transmissionrequest signal RTS), thereby notifying a communication request to thelens microprocessor 111.

Upon detecting the communication request by the voltage level oftransmission request signals RTS having changed to Low, the lensmicroprocessor 111 preforms generating processing of lens data signalsDLC to transmit to the camera microprocessor 205. Once transmissionpreparation of the lens data signals DLC has been made, transmission ofone frame of lens data signals DLC is started via the first datacommunication channel. Now, the lens microprocessor 111 startstransmission of the lens data signals DLC within the set time that hasbeen mutually set between the camera microprocessor 205 and the lensmicroprocessor 111, from the point in time that the voltage level of thetransmission request signals RTS has gone to Low.

That is to say, it is sufficient in the communication method B for thelens data to be transmitted to be finalized between the point in timethat the voltage level of the transmission request signals RTS goes toLow up to transmission of the lens data signals DLC being started. Thereare no strict restrictions as with the communication method A, where thelens data to be transmitted has to be finalized by the point in time atwhich the first clock pulse is input, so the timing at which to starttransmitting the lens data signals DLC can be given more freedom.

Next, the camera microprocessor 205 returns the voltage level of thetransmission request signals RTS to High, in accordance with detectionof the start bit ST added to the head of the lens data signals DLC dataframe received from the lens microprocessor 111. Hereafter, this will bereferred to as negating the transmission request signal RTS.Accordingly, the transmission request is cancelled, and transmission ofthe camera data signals DCL over the second communication channel isstarted. Note that either of negating transmission request signals RTSand starting transmission of camera data signals DCL may be first, andthat it is sufficient for this to be performed by the time thatreception of the lens data signals DLC data frame is completed.

In a case where the lens microprocessor 111 that has transmitted thelens data signals DLC data frame needs to notify the cameramicroprocessor 205 of a communication standby request BUSY, a BUSY frameis added to the lens data signals DLC. The camera microprocessor 205monitors whether or not there are communication standby request BUSYnotifications, and asserting transmission request signals RTS isforbidden while a communication standby request BUSY is being notified,for the next transmission request.

The lens microprocessor 111 executes necessary processing during theperiod where communication from the camera microprocessor 205 has beenput on standby by the communication standby request BUSY, and thecommunication standby request BUSY is cancelled after preparation forthe next communication is ready. The camera microprocessor 205 ispermitted to assert transmission request signals RTS for the nexttransmission request, under the conditions that the communicationstandby request BUSY has been cancelled and that transmission of thecamera data signals DCL data frame has been completed.

Thus, according to the present embodiment, the lens microprocessor 111starts transmission of a lens data signals DLC data frame to the cameramicroprocessor 205 in accordance with transmission request signals RTShaving been asserted with a communication start event at the cameramicroprocessor 205 as a trigger. The camera microprocessor 205 thenstarts transmission of a camera data signals DCL data frame to the lensmicroprocessor 111 in accordance with having detected the start bit STof the lens data signals DLC.

The lens microprocessor 111 adds a BUSY frame after the lens datasignals DLC data frame for a communication standby request BUSY asnecessary, and hereafter cancels the communication standby request BUSY,thereby completing communication processing of one frame. According tothis communication processing, one byte of communication data ismutually exchanged between the camera microprocessor 205 and lensmicroprocessor 111.

Next, the communication mode M3 where communication is performed by theformat F2 using the communication method B will be described. FIG. 5Aillustrates waveforms of the communication signals exchanged between thecamera microprocessor 205 and lens microprocessor 111 in thecommunication mode M3. In FIG. 5A, the waveforms for communicationsignals in a case of consecutively transmitting three frames of data areillustrated. Adding a communication standby request BUSY to lens datasignals DLC is forbidden in format F2, as described earlier.

In the lens data signals DLC data format in the communication mode M3,one frame is made up of a data frame alone, and here is no BUSY frame.Accordingly, the lens microprocessor 111 cannot notify the cameramicroprocessor 205 of a communication standby request BUSY in thecommunication mode M3.

This format F2 is used for usages of performing continuous communicationwith reduced inter-frame intervals, when transferring relatively largeamounts of data between the camera microprocessor 205 and lensmicroprocessor 111. That is to say, the format F2 enables large amountsof data to be communicated at high speeds.

Next, the communication control processing between the cameramicroprocessor 205 and lens microprocessor 111 that is a feature of thepresent embodiment will be described. FIG. 5B illustrates waveforms ofcommunication signals when each of the camera microprocessor 205 andlens microprocessor 111 consecutively transmit and receive n frames ofcamera data signals DCL and lens data signals DLC. The cameramicroprocessor 205 asserts transmission request signals RTS when anevent of starting communication with the lens microprocessor 111 occurs.In the format F2, the camera microprocessor 205 does not need to negatethe transmission request signals RTS in each frame, unlike with theformat F 1. Accordingly, the state of asserting transmission requestsignals RTS is maintained as long as a state where data can beconsecutively transmitted/received.

Upon detecting a communication request by asserting of transmissionrequest signals RTS, the lens microprocessor 111 performs processing togenerate lens data signals DLC to transmit to the camera microprocessor205. Once preparation for transmission of the lens data signals DLC isready, transmission of the first frame of lens data signals DLC (DL1) isstarted over the first data communication channel.

The lens microprocessor 111 that has transmitted the first frame of thelens data signals DLC data frame confirms the transmission requestsignals RTS again. In a case where the transmission request signals RTSare in an asserted state, the lens microprocessor 111 transmits thesecond frame of lens data signals DLC (DL2) to the camera microprocessor205 in succession after the first frame of which transmission has beencompleted. Thus, the lens data signals DLC (DL1 through DLn) aresuccessively transmitted to the camera microprocessor 205 from the lensmicroprocessor 111 as long as the asserted state of transmission requestsignals RTS is maintained. Once transmission of the predetermined numberof frames n has been completed, transmission of lens data signals DLC isstopped.

In response to detection of the start bit ST for each frame of lens datasignals DLC from the lens microprocessor 111 being detected, the cameramicroprocessor 205 starts transmission of n frames of camera datasignals DCL (DC1 through DCn) over the second communication channel.

FIG. 5C illustrates waveforms of communication signals in a case where atemporary communication standby has been instructed from the cameramicroprocessor 205 or lens microprocessor 111 during the communicationof consecutive data exchange illustrated in FIG. 5B. In this case aswell, the lens microprocessor 111 starts transmission of lens datasignals DLC due to transmission request signals RTS being asserted bythe camera microprocessor 205, and the camera microprocessor 205 startstransmission of camera data signals DCL in accordance with detection ofa start bit ST thereof.

T2w1 indicates a communication standby period that is a period regardingwhich communication standby has been instructed from the cameramicroprocessor 205, this instruction being notified to the lensmicroprocessor 111 by temporary negation of transmission request signalsRTS. Upon detecting that the transmission request signals RTS have beennegated, the lens microprocessor 111 pauses transmission after havingcompleted transmission of the frame of lens data signals DLC that isbeing transmitted at the time of detection (DL6 in the drawing:hereinafter referred to as a pause frame).

In response to the pausing of transmission of lens data signals DLC, thecamera microprocessor 205 also pauses transmission of the camera datasignals DCL after having transmitted the frame corresponding to theabove pause frame (DC6), out of the camera data signals DCL. Accordingto this communication control, management can be performed so that thenumber of transmitted frames of lens data signals DLC and camera datasignals DCL can be made to be the same even if a communication standbyinstruction occurs during communication of consecutive data exchange.

Once the communication standby request event is gone, the cameramicroprocessor 205 can instruct resuming of communication to the lensmicroprocessor 111, by asserting the transmission request signals RTSagain. Transmission of lens data signals DLC by the lens microprocessor111 is resumed from the next frame (DL7: hereinafter referred to asresume frame) after the pause frame, in accordance with thecommunication resume instruction. Upon detecting the start bit ST of theresume frame, the camera microprocessor 205 resumes transmission ofcamera data signals DCL from the frame (DC7) corresponding to the resumeframe above.

On the other hand, T2w2 represents a communication standby period whichis a period that communication standby has been instructed by the lensmicroprocessor 111. After ending of the communication standby periodT2w1 in the drawings, neither the camera microprocessor 205 nor the lensmicroprocessor 111 has instructed communication standby, and theabove-described resume frames DL7 and DC7, and subsequent frames DL8,DC8 through DL9, and DC9, are subjected to consecutive datatransmission/reception, in that order.

When transmission of frame DL9 within the lens microprocessor 111(reception of the frame DC9 at the camera microprocessor 205) iscompleted, a communication standby request event occurs, whereby thelens microprocessor 111 notifies the camera microprocessor 205 of acommunication standby instruction. When the transmission request signalsRTS are in an asserted state, the lens microprocessor 111 does nottransmit lens data signals DLC, thereby notifying the cameramicroprocessor 205 from the lens microprocessor 111 that communicationwill be paused.

The camera microprocessor 205 constantly monitors the start bit ST ofeach frame in the lens data signals DLC, and is stipulated such that, ina case where the start bit ST is not detected, transmission of the nextframe of camera data signals DCL is stopped. In a case where the cameramicroprocessor 205 does not receive lens data signals DLC from the lensmicroprocessor 111 (DL10 in the drawing) even though it is assertingtransmission request signals RTS, communication is paused withouttransmitting the camera data signals DCL (DC10). Note that the cameramicroprocessor 205 maintains the transmission request signals RTS in anasserted state during the communication standby period T2w2 underinstruction from the lens microprocessor 111.

Thereafter, the communication standby request event in the lensmicroprocessor 111 is gone, and the lens microprocessor 111 resumestransmission of the resume frame DL10 of the lens data signals DLC. Thecamera microprocessor 205 resumes transmission of the correspondingframe DC10 in the camera data signals DCL in accordance with havingdetected the start bit ST of this resume frame DL10.

Next, the procedures of deciding the communication format performedbetween the camera microprocessor 205 and the lens microprocessor 111will be described with reference to FIG. 6. The camera microprocessor205 and lens microprocessor 111 perform the communication control of theflowcharts in FIGS. 6 and 7, following a communication control programthat is a computer program. Note that “S” in FIGS. 6 and 7 means step.

First, when the interchangeable lens 100 is mounted to the camera mainbody 200, in step S100 and step S200 the camera microprocessor 205 andlens microprocessor 111 set the communication format to an initialcommunication format, regarding which establishing communication isguaranteed. The initial communication format here may be a combinationof communication method and data format disclosed in the presentembodiment, or may be another communication format. In a case where anasynchronous communication format is selected as the initialcommunication format, a BUSY identification position P is preferablyset, so that communication can be executed between any combination ofcamera and interchangeable lens.

Next, in step S101, the camera microprocessor 205 transmits cameraidentification information, representing communication formats that thecamera main body 200 is capable of handling, to the lens microprocessor111. Also, in step S202, the lens microprocessor 111 transmits lensidentification information, representing communication formats that theinterchangeable lens 100 is capable of handling, to the cameramicroprocessor 205.

The “identification information” here includes information indicatingwhich of the clock-synchronized method and the asynchronous method thereis compatibility with, and information indicating the range ofcommunication bitrates that can be handled. Information indicating theBUSY identification position P is also included in the identificationinformation.

The camera microprocessor 205 receives the lens identificationinformation in step S102. The lens microprocessor 111 receives thecamera identification information in step S201. Although the lensidentification information is transmitted after the cameraidentification information is transmitted in the flowchart in FIG. 6,the transmission of the camera identification information and thetransmission of the lens identification information may be at the sametime. Further, the camera identification information may be transmittedafter the lens identification information is transmitted.

Next, in step S103 and step S203, the communication format to be used insubsequent communication is set. Specifically, the camera microprocessor205 and lens microprocessor 111 decide, out of the communicationbitrates that each other can handle, the fastest rate as thecommunication bitrate. Also, a position out of BUSY identificationpositions that each other is capable of handling, that is closest to thestop bit SP, is set as the BUSY identification position.

Next, a data communication flow in the asynchronous communication methodwill be described with reference to FIG. 7. FIG. 7 describes acommunication flow in a data format where adding a BUSY signal ispermitted.

The camera microprocessor 205 monitors whether or not a communicationevent for starting communication with the lens microprocessor 111 hasoccurred, and in a case where a communication event has occurred in stepS110, advances to step S111. Transmission request signals RTS areasserted in step S111 as described so far, thereby placing acommunication request with the lens microprocessor 111.

The lens microprocessor 111 monitors whether or not there has beenassertion of transmission request signals RTS, and upon recognizing thatthere has been assertion of transmission request signals RTS in stepS210, advances to step S211. In step S211, the lens microprocessor 111transmits lens data signals DLC to the camera microprocessor 205 via thefirst data communication channel.

Upon receiving lens data signals DLC from the lens microprocessor 111(YES in step S112), the camera microprocessor 205 advances to step S113,and negates transmission request signals RTS. The flow then advances tostep S114, and camera data signals DCL are transmitted to the lensmicroprocessor 111 via the second data communication channel.

Upon detecting start of reception of camera data signals DCL in stepS212, the lens microprocessor 111 advances to step S213, and performsreception processing of the camera data signals DCL. In parallel withthe processing of step S213, determination is made in step S214regarding whether or not there is need to notify the cameramicroprocessor 205 of a communication standby request BUSY. In a casewhere there is no need to make notification of a communication standbyrequest BUSY, the flow advances to step S218, and stands by untilreception of the camera data signals DCL ends.

On the other hand, in a case where there is a need for the lensmicroprocessor 111 to notify the camera microprocessor 205 of acommunication standby request BUSY, the flow advances to step S215, anda BUSY frame is added to the lens data signals DLC. The lensmicroprocessor 111 executes necessary processing while notification ofthe communication standby request BUSY is being notified, and afterpreparation for the next communication has been completed (Yes in stepS216), the communication standby request BUSY is cancelled (step S217).After having canceled the communication standby request BUSY, the flowadvances to step S218, and stands by until reception of the camera datasignals DCL is completed. Upon reception of the camera data signals DCLis complete (Yes in step S218), the flow returns to step S210, andmonitoring of whether transmission request signals RTS have beenasserted is continued.

Upon having received the communication standby request BUSY in stepS115, the camera microprocessor 205 stands by until the communicationstandby request BUSY is cancelled. When the communication standbyrequest BUSY is cancelled (YES in step S116), the flow advances to stepS117, and determination is made regarding whether or not transmission ofthe camera data signals DCL has been completed. Even in a case wherenotification of a communication standby request BUSY has not beenreceived in step S115, the flow advances to step S117, and determinationis made regarding whether or not transmission of the camera data signalsDCL has been completed. If determination is made in step S117 thattransmission of the camera data signals DCL has been completed, the flowreturns to step S110, and monitoring of whether or not a communicationevent has occurred is continued.

As described above, the present embodiment relates to communicationcontrol in asynchronous (communication method B) communication made upof three channels. A communication standby request BUSY is transmittedfrom the lens microprocessor 111 to the camera microprocessor 205, viathe first data communication channel that is a dedicated output channelof the lens microprocessor 111. On the other hand, a transmissionrequest signals RTS from the camera microprocessor 205 is transmittedfrom the camera microprocessor 205 to the lens microprocessor 111 viathe notification channel serving as a dedicated output channel of thecamera microprocessor 205.

Thus, the communication standby request BUSY from the lensmicroprocessor 111 is exchanged via the dedicated output channel of thelens microprocessor 111, and the transmission request signal RTS fromthe camera microprocessor 205 is exchanged via the dedicated outputchannel of the camera microprocessor 205. Accordingly, thecommunication-invalid period between the camera microprocessor 205 andlens microprocessor 111 can be shortened, and as a result, effectivecommunication speed can be increased.

With regard to the start timing of communication, data transmission fromthe lens microprocessor 111 to the camera microprocessor 205 is startedfirst. The camera microprocessor 205 starts data transmission inaccordance with having detected a start bit ST of a data frametransmitted from the lens microprocessor 111. Setting the start timingfor communication in this way enables the lens microprocessor 111, whichhas received the transmission request signal RTS, to have freedom in thetiming for starting data transmission to the camera microprocessor 205.

For example, the start timing for data transmission can be changed inaccordance with the information processing capabilities of the lensmicroprocessor 111. Accordingly, the communication speed between thecamera main body 200 and the interchangeable lens 100 can be improvedwithout leading to breakdown of communication.

The above-described embodiment is only a representative example, andvarious modifications and alterations may be made to the embodimentswhen carrying out the present invention. For example, although anexample of using an interchangeable lens as the accessory device hasbeen illustrated in the above embodiment, a strobe or the like may beused as long as having function of communicating with the imagingapparatus.

The present invention can also be realized by processing of a programrealizing one or more of functions of the above-described embodimentbeing supplied to a system or apparatus via a network or recordingmedium, and one processor or more in the system or apparatus in thecomputer reading out and executing the program. This can also berealized by a circuit having one or more function (e.g., an ASIC).

According to the present invention, an accessory device and imagingapparatus capable of performing high-speed data exchange without leadingto breakdown of communication, without adding new channels, can beobtained.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

1. An accessory device detachably mountable to an imaging apparatus, theaccessory device comprising: an accessory communication circuitry thatprovides, between itself and the imaging apparatus, a notificationchannel used for notification from the imaging apparatus to theaccessory device, an accessory data communication channel used for datatransmission from the accessory device to the imaging apparatus, and animaging apparatus data communication channel used for data transmissionfrom the imaging apparatus to the accessory device; and an accessorycontrol circuitry configured to control the accessory communicationcircuitry.
 2. The accessory device according to claim 1, wherein theaccessory control circuitry transmits a first data to the imagingapparatus via the accessory data communication channel, in response toreceiving, via the notification channel, a transmission request signal,the transmission request signal being a signal for requestingtransmission of data from the accessory device to the imaging apparatus,and receives, via the imaging apparatus data communication channel, asecond data transmitted, to the accessory device, from the imagingapparatus in response to the imaging apparatus starting to receive thefirst data.
 3. The accessory device according to claim 2, wherein aperiod to transmit the first data and a period to receive the seconddata are partially overlapped.
 4. The accessory device according toclaim 2, wherein the accessory control circuitry starts receiving of thesecond data after starting transmission of the first data.
 5. Theaccessory device according to claim 4, wherein the accessory controlcircuitry starts receiving of the second data after transmitting a startbit included in the first data.
 6. The accessory device according toclaim 2, wherein the transmission request signal is expressed bychanging a voltage level of the notification channel.
 7. The accessorydevice according to claim 6, wherein the accessory control circuitrytransmits the first data within a predetermined period after the voltagelevel of the notification channel changes.
 8. The accessory deviceaccording to claim 6, wherein the transmission request signal isexpressed by changing the voltage level of the notification channel froma first level to a second level which is different from the first level,and the accessory control circuitry transmits a third data to theimaging apparatus, via the accessory data communication channel, in acase where the voltage of the notification channel is the second levelafter transmitting the first data.
 9. The accessory device according toclaim 2, wherein the accessory device performs communication with theimaging apparatus by switching between a data format where data framesare transmitted without a communication standby period, and a dataformat where data frames are transmitted with a communication standbyperiod.
 10. The accessory device according to claim 9, wherein in a casewhere the communication format, between itself and the imagingapparatus, is the data format where data frames are transmitted with thecommunication standby period, a number of data which the accessorycontrol circuitry transmitted to the imaging apparatus before thecommunication standby period and a number of data which the accessorycontrol circuitry received from the imaging apparatus before thecommunication standby period are the same number.
 11. The accessorydevice according to claim 9, wherein the transmission request signal isexpressed by changing the voltage level of the notification channel froma first level to a second level which is different from the first level,and the communication standby period is expressed by the voltage levelof the notification channel in the first level.
 12. The accessory deviceaccording to claim 9, wherein the accessory control circuitry pausesdata transmission to the imaging apparatus while the communicationstandby request event occurring in the accessory device.
 13. Theaccessory device according to claim 2, wherein the accessory deviceperforms an asynchronous communication with the imaging apparatus. 14.The accessory device according to claim 2, wherein the accessory deviceis communicable with the imaging device by switching communicationmethods between a clock-synchronized communication method synchronizedwith clock signals and an asynchronous communication method, and theaccessory control circuitry receives, via the notification channel, theclock signals transmitted from the imaging device in theclock-synchronized communication method, and receives, via thenotification channel, the transmission request signal in theasynchronous communication method.
 15. The accessory device according toclaim 2, wherein the accessory device comprises an imaging opticalsystem capable of forming a subject image on an imaging device of theimaging apparatus.
 16. An imaging apparatus to which an accessory deviceis detachably mounted, the apparatus comprising: an imaging apparatuscommunication circuitry provided with, between itself and the accessorydevice, a notification channel used for notification from the imagingapparatus to the accessory device, an accessory data communicationchannel used for data transmission from the accessory device to theimaging apparatus, and an imaging apparatus data communication channelused for data transmission from the imaging apparatus to the accessorydevice; and an imaging apparatus control circuitry configured to controlthe imaging apparatus communication circuitry.
 17. The imaging apparatusaccording to claim 16, wherein the imaging apparatus control circuitrytransmits, via the notification channel, a transmission request signalto the accessory device, the transmission request signal being a signalfor requesting data transmission from the accessory device to theimaging apparatus, and transmits a second data to the accessory device,via the imaging apparatus data communication channel, in response tostarting to receive a first data transmitted, to the imaging apparatus,from the accessory device according to the transmission request signal.18. The imaging apparatus according to claim 17, wherein a period toreceive the first data and a period to transmit the second data arepartially overlapped.
 19. The imaging apparatus according to claim 17,wherein the imaging apparatus control circuitry starts transmitting thesecond data in response to reception of a start bit included in thefirst data.
 20. The imaging apparatus according to claim 17, wherein theimaging apparatus control circuitry transmits the transmission requestsignal to the accessory device by changing a voltage level of thenotification channel.
 21. The imaging apparatus according to claim 20,wherein the imaging apparatus control circuitry transmits thetransmission request signal by changing the voltage level of thenotification channel from a first level to a second level which isdifferent from the first level, and the imaging apparatus controlcircuitry receives a third data from the accessory device, via theaccessory data communication channel, by maintaining the voltage of thenotification channel at the second level during and after receiving thefirst data.
 22. The imaging apparatus according to claim 17, wherein theimaging apparatus performs communication with the accessory device byswitching between a data format where data frames are transmittedwithout a communication standby period, and a data format where dataframes are transmitted with a communication standby period.
 23. Theimaging apparatus according to claim 22, wherein in a case thecommunication format, between itself and the accessory device, is thedata format where data frames are transmitted with the communicationstandby period, a number of data which the imaging apparatus controlcircuitry transmitted to the accessory device before the communicationstandby period, and a number of data which the imaging apparatus controlcircuitry received from the accessory device before the communicationstandby period are the same number.
 24. The imaging apparatus accordingto claim 22, wherein the imaging apparatus control circuitry transmitsthe transmission request signal by changing the voltage level of thenotification channel from a first level to a second level which isdifferent from the first level, and the imaging apparatus controlcircuitry notifies the communication standby period to the accessorydevice by setting the voltage level of the notification channel to thefirst level.
 25. The imaging apparatus according to claim 17, whereinthe imaging apparatus control circuitry performs an asynchronouscommunication with the accessory device.
 26. The imaging apparatusaccording to claim 17, wherein the imaging apparatus is communicablewith the accessory device by switching communication methods between aclock-synchronized communication method synchronized with clock signalsand an asynchronous communication method, and the imaging apparatuscontrol circuitry transmits the clock signals to the accessory device,via the notification channel, in the clock-synchronized communicationmethod, and transmits the transmission request signal to the accessorydevice, via the notification channel, in the asynchronous communicationmethod.
 27. An imaging system including an imaging apparatus and anaccessory device detachably mountable to the imaging apparatus, whereinthe accessory device comprises: an accessory communication circuitryhaving, between itself and the imaging apparatus, a notification channelused for notification from the imaging apparatus to the accessorydevice, an accessory data communication channel used for datatransmission from the accessory device to the imaging apparatus and animaging apparatus data communication channel used for data transmissionfrom the imaging apparatus to the accessory device; and an accessorycontrol circuitry configured to control the accessory communicationcircuitry, wherein the imaging apparatus comprises: an imaging apparatuscommunication circuitry having, between itself and the accessory device,the notification channel, the accessory data communication channel andthe imaging apparatus data communication channel; and an imagingapparatus control circuitry configured to control the imaging apparatuscommunication circuitry.